Tubular obstruction by desquamated epithelial cells plays a critical role in the development of acute renal failure. A recent observation that viable renal tubular cells rather than cellular debris can be recovered from urine of patients with acute tubular necrosis, prompted an investigation into a possible defect in cell adhesion to the basement membrane. The hypothesis to be tested in the current research proposal is that loss of focal adhesions precipitates cell detachment from the basement membrane, while the concomitant reorientation of adhesion molecules, notably integrins, from their basal location to the apical cell surface results in adhesion of dislodged cells to the remaining epithelial layer and/or conglomeration of detached cells, both events culminating in tubular obstruction. The hypothesis will be tested by exploring three experimental aims: (1) To examine the mechanisms governing stress-induced cell detachment from the matrix, notably redistribution of integrin receptors and the role of protein kinases, cytosolic calcium, and the cytoskeleton in this process; (2) To study mechanisms of cell-cell adhesion of detached cells and attachment of dislodged cells to the epithelial layer; and (3) To evaluate the model of tubular obstruction in vivo and to examine the effect of maneuvers designed to reduce cell-cell adhesion and/or cell detachment on renal function after induction of acute ischemic or nephrotoxic injury. Cultured renal epithelial cells of primate origin (BSC-1) will constitute the in vitro model while whole animal models of acute renal failure will be used to corroborate the in vitro findings. The major techniques used in this study include intravital immunocytochemistry, interference reflection microscopy combined with microinjection of rhodamine phalloidin, digital ratio image analysis and confocal microscopy, FACS analysis, cell-matrix attachment assay, cell- cell attachment assay, molecular biological approaches for analysis of integrin mRNA. The results obtained in this research proposal will be integrated into a unifying hypothesis that will shed new light on the pathophysiologic mechanisms inducing tubular obstruction and acute renal compromise and outline potential methods of therapeutic intervention.